Stephen Krashen introduced the “Monitor Model” to the field in 1970, which encompassed five unique hypotheses that saught to provide new perspectives on how students acquired second languages. It is important to note that the term second language in this context refers to any language learned after an individual’s first language (their L1). This means that a second language (the L2) can indeed be the second language learned, or the third, fourth, fifth, etc. To get a better understanding of the Monitor Model, let’s jump into each of the hypotheses behind Krashen’s work. Much of the details behind this analysis have been derived from How Languages are Learned by Patsy Lightbown and Nina Spada².

First, Stephen Krashen puts an emphasis on the concept that language is not directly learned but rather acquired through useful and comprehensible inputs. This falls under his acquisitional learning hypothesis, which begins the process of the metaphorical and cognitive ‘system’ created from input that a learner of language accesses for output. The idea of comprehensible input is key, and will be expanded upon by Krashen later within this model.

The next hypothesis presented under the Monitor Model is the monitor hypothesis. Within this hypothesis, it is proposed that learners access the system developed under the acquisitional learning hypothesis through “spontaneous conversation.”³ A few rules apply to effective spontaneous conversation, such as the active process that a learner or interlocutor may take to monitor the generated output by the learner. By being concerned that the output is correct, the access to a learner’s mental language system can then strengthen acquired knowledge in conjunction with the grammatical rules and structures that were explicitly learned by the learner through instruction.

Similarly to the procedures followed by a learner during the acquisition of the first language, there is potentially an identifiable order behind the sequences that a learner takes during the acquisition of their L2. This idea is encompassed in Krashen’s natural order hypothesis, which highlights the idea that second language learners will understand concepts in their target language in order of difficulty. In the first language, an example of this would be the development allowing one to differentiate between phonetic such as the sounds behind “no” and “mo.”⁴ Similarly, a language learner targeting Korean may be able to first identify the difference between “자” (ja) and “차” (cha).

Onwards with comprehensible input, Krashen’s comprehensible input hypothesis provides a guide for instruction in relation to the ideas of active learning and appropriate challenge levels for students. Within this, he states that acquisition of language happens when there is input provided to the learner that they are able to make sense of, along with this input following the formula i+1. The variable i in this formula represents the language system that is already developed (and acquired) by the learner, and the +1 stands in place for the parts of language that is merely a step above the learner’s current level. This incites the continuation of learning for the learner, and ensures that they are being given adequate challenge that is not too far outside of their current zone of proximal development.

Finally, the Monitor Model touches upon a student’s affect and the complex dynamic system theory. By understanding a student’s affective domain and how this plays into the complex dynamic system theory (a theory that highlights the concept that a student’s motivation is not static by any means, but rather is dynamic based upon context and time⁵), instructors are able to better model their learning experiences to avoid overwhelming their learners. Krashen recognizes this within his Affective Filter Hypothesis, which states that when a student is “…tense, anxious, or bored (they) may filter out input, making it unavailable for acquisition”.⁶